RTT optimization: 8kHz support, io_uring backend option (tested slower), RT-promote tx_rx thread; 8kHz RTT min 0.75ms mean 1.04ms

Cargo.toml

@@ -7,7 +7,7 @@ license = "MIT OR Apache-2.0"
 description = "J1900 <-> TwinCAT 1 kHz communication verification over an EL6695 EtherCAT bridge"
 
 [dependencies]
-ethercrab = { version = "0.7", default-features = false, features = ["std"] }
+ethercrab = { version = "0.7", default-features = false, features = ["std", "io-uring"] }
 futures-lite = "2"
 libc = "0.2"
 crc32fast = "1.4"

src/main.rs

@@ -19,7 +19,7 @@ use std::time::{Duration, Instant};
 
 use el6695_rt::{bridge, regs, rt, stats};
 use ethercrab::{
-    std::{ethercat_now, tx_rx_task},
+    std::{ethercat_now, tx_rx_task, tx_rx_task_io_uring},
     MainDevice, MainDeviceConfig, PduStorage, Timeouts,
 };
 use stats::OnlineStats;
@@ -101,6 +101,8 @@ struct Config {
     /// Enable DC SYNC0 on the EL6695 secondary (cycle = --cycle-us) and print
     /// per-second DC phase/drift telemetry in the report line.
     dc: bool,
+    /// Use the io_uring-based blocking TX/RX loop instead of AF_PACKET poll.
+    iouring: bool,
 }
 
 fn parse_args() -> Result<Config, String> {
@@ -120,6 +122,7 @@ fn parse_args() -> Result<Config, String> {
         el1252_every: 1,
         spin: false,
         dc: false,
+        iouring: false,
     };
     let mut args = std::env::args().skip(1).peekable();
     if let Some(a) = args.peek() {
@@ -151,6 +154,7 @@ fn parse_args() -> Result<Config, String> {
             "--quiet" => cfg.quiet = true,
             "--spin" => cfg.spin = true,
             "--dc" => cfg.dc = true,
+            "--iouring" => cfg.iouring = true,
             "--el2202" => cfg.el2202 = true,
             "--el2202-dual" => {
                 cfg.el2202 = true;
@@ -236,11 +240,22 @@ async fn run(cfg: &Config) -> Result<(), Box<dyn std::error::Error>> {
     );
 
     let iface = cfg.iface.clone();
+    let use_iouring = cfg.iouring;
     let _txrx = std::thread::spawn(move || {
+        if let Err(e) = rt::promote_current_thread(1, 79, false) {
+            eprintln!("tx_rx RT promotion failed (continuing): {}", e);
+        }
+        if use_iouring {
+            match tx_rx_task_io_uring(&iface, tx, rx) {
+                Ok(_) => {}
+                Err(e) => eprintln!("io_uring tx_rx task ended with error: {:?}", e),
+            }
+        } else {
             let task = tx_rx_task(&iface, tx, rx).expect("create tx_rx task");
             if let Err(e) = futures_lite::future::block_on(task) {
                 eprintln!("tx_rx task ended with error: {:?}", e);
             }
+        }
     });
 
     println!("Scanning segment (INIT -> PREOP)...");